NO317016B1 - Procedure for fractionation of oats, as well as stable, soluble oat protein fractions. - Google Patents

Description

The present invention relates to a method for fractionating oats, as well as stable, soluble oat protein fractions. The process results in the production of a transparent, stable oat protein-containing, aqueous solution with a low fat content. The present invention also applies to the aqueous solution product according to the method and a stable, soluble oat protein fraction which, when brought into solution, gives a transparent, stable, oat protein-containing, aqueous solution.

The oat seed from which the oat comb is taken comprises an oat husk and an oat groat. The oat husk serves as an outer covering for the grits. Oat groats consist of oat bran, including the seed coat and aleurone layers, germ and seed white. It is desirable to fractionate the oat groats into its soluble and insoluble fractions, because each fraction of the groats has a value in itself. Of particular interest in the present invention is the water-soluble fraction of the groats, including its water-soluble oat protein fraction. The soluble oat protein fraction has many useful applications, including use in cosmetics, in hair and skin care preparations such as bath water, shampoos, creams and gels, ready-to-eat cereal products to improve their taste and texture and when preparing meals for regulated diets such as reduced hospital meals, baby food and special nutritious preparations such as e.g. drinks with a high protein content.

Oat protein also has a greater nutritional value than other cereal proteins due to its greater and more balanced concentration of essential amino acids. Amino acids are essential for human life because they are the basic materials for the production of the necessary protein. If the oat protein can be isolated, one has a suitable material for increasing the protein content in a number of foodstuffs or for forming a desirable protein component. Also of interest are oat protein-containing, low-fat aqueous solutions and solid mixtures used to prepare aqueous solutions. These can be used as additives and protein additives in foods with a low fat content. It is also believed that such oat protein-containing preparations and low-fat mixtures will be more stable, since they are less likely to be subject to rancidity. This is because they contain less fat that can be oxidized, which is the cause of rancidity. Unfortunately, such oat protein-containing preparations with a low fat content are also translucent, and are therefore not aesthetically pleasing when added to clear preparations such as e.g. drinks.

Oat protein-containing solutions with a low fat content also have a greater concentration of protein than full-fat preparations. This gives a greater protein yield, and the corresponding economy in an efficient operation.

In view of the above, it would be desirable to produce a transparent, oat protein-containing, aqueous solution and a solid mixture which is transparent in solution, and which can be used in clear cosmetics and hair and skin care preparations. It would also be desirable if such an aqueous solution and a solid mixed fraction also had a low fat content. Until today, however, the known methods for producing oat protein-containing, aqueous preparations and solid mixtures give products that are not clear, and therefore cannot be used in such preparations.

With these advantages, it would be desirable to produce a water-soluble oat protein fraction, as well as an aqueous solution containing such a fraction. However, oat protein fractions are typically unstable, in that they tend to fall out of suspension in an aqueous environment. Moreover, even when relatively stable, oat protein fractions and aqueous preparations containing such fractions are produced by methods which are undesirable and yield products which are undesirable. In particular, oat protein fractions, aqueous preparations containing such fractions and methods for the preparation of such fractions and preparations described tend to yield a protein which is substantially insoluble when dried, must be treated for a very long time, allowing the growth of undesirable microbes that can contaminate the final product and/or form translucent suspensions, which limits their use to some extent. Therefore, it is desirable to obtain a soluble oat protein fraction which is stable, which can preferably be prepared by means of a method which is not too time-consuming and which provides a transparent, aqueous solution when in solution, which enables a wider use of the product.

The present invention provides a transparent, stable, low-fat oat protein-containing solution, a solid, stable, low-fat oat protein fraction that provides a transparent, aqueous solution upon rehydration, and a method for producing such an aqueous solution and solid mixture.

The present invention provides such products, as well as a method for producing them.

The state of the art describes methods for fractionating oats and products from these methods.

US Patent 4,028,468 describes a process for fractionating oats comprising grinding dried, dehulled oat groats to form an oat flour containing a dense, fine fraction of regularly shaped particles and a light, coarse fraction of irregularly shaped particles, wherein the coarse fraction includes oat bran, oat gum, oat protein and oat starch. The flour is recovered and the coarse and fine fractions are separated. The coarse fraction is then recovered and a heated basic slurry containing the recovered coarse fraction is prepared. The heated basic slurry is shaken to perform an extraction and to form a clay fraction and a soluble fraction containing the oat gum, oat protein and oat starch. The oat bran is then recovered from the slurry while the oat gum, oat protein and oat starch remain in the soluble fraction, thereby forming an alkaline extract of the soluble fraction. The alkaline extract is then cooled to a temperature in the range from approx. the freezing point of the alkaline extract to ambient temperature. The alkaline extract is cooled to form a precipitate of oat protein, which is removed together with the starch from the extract to form a supernatant liquid containing the oat gum, thereby recovering the protein precipitate and the starch. The supernatant liquid is neutralized and heated to at least 90°C, after which the oat gum is recovered.

US patent 4,448,790 describes a method for fractionating grain flour into at least three food grade fractions including starch, protein and sugar fractions. The claimed method comprises slurrying grain flour in water, separating the resulting slurry into a heavier fraction containing ordinary grain starch with a larger particle size and a lighter fraction containing approx. 15 to 40% of the dry matter in the flour which contains protein-coated small starch particles, heating the lighter fraction to a temperature of at least 120°C for a period of time sufficient for the protein network on the surface of the small starch particles to break down and the starch to gelatinize , cooling the lighter fraction to a temperature of 90°C or lower and treating said lighter fraction simultaneously with α-amylase and R-glucanase, separating the resulting protein precipitate from the lighter fraction as a precipitate to obtain a clear fraction which remains after separation of the precipitate and saccharification of the clear fraction with amyloglucosidase or fungal amylase at a temperature of 55°C or lower until the dextrose equivalent is at least 20-80.

US patent 4 377 602 describes a method for producing a hydrolysed protein and starch product from whole grains and a product according to the method. In the described method, enzymatically hydrolyzed protein and starch products are produced from whole grain in situ, which method comprises crushing whole grain and then subjecting the crushed grain to a treatment which essentially consists of the following steps: the grain is subjected to an enzymatic treatment in an aqueous medium with an endopeptidase to convert substantially all water-insoluble proteins in the grain to water-soluble protein products, which are then filtered and recovered from the crushed grain as a clear filtrate containing protein products containing peptides and amino acid residues and subjecting the remaining crushed grain to an enzymatic treatment in an aqueous medium with barley amylase followed in sequence by an amyloglucosidase, both enzymes being substantially free of other carbohydrate-hydrolyzing enzymes to convert substantially all of the water-insoluble starch fraction in the grain to water-soluble starch breakdown products , in which amylogl ukosidase is at a pH value of between 4 and 4.5, to convert essentially all of the water-insoluble starch fractions in the grain into glucose.

US patent 4,282,319 describes a method for producing a hydrolyzed protein and starch product from whole grain and a product according to the method. In the described method, enzymatically hydrolyzed protein and starch products are produced from whole grain in situ, which method comprises grinding whole grain and then subjecting the milled grain to a treatment which essentially consists of the following steps: the grain is subjected to an enzymatic treatment in an aqueous medium with an endopeptidase to convert substantially all water-insoluble proteins present in the grain into water-soluble protein products, which are then filtered and recovered from the crushed grain as a clear filtrate containing protein products containing peptides and amino acid residues and exposing the remainder, crushing the grain for an enzymatic treatment in an aqueous medium with at least one starch-hydrolyzing enzyme to convert substantially all of the water-insoluble starch fraction in the grain to water-soluble, degraded products of starch, and wherein the starch-hydrolyzing enzyme is amylase which is substantially free from other carbohy drat-hydrolyzing enzymes.

In the articles "Functional Properties of Oat Concentrate Treated With Linoleate or Trypsin", C. Ma, J. Inst. Can. Pollock. Technol. Aliment., vol. 18, No. 1, pp. 79-84

(1985) and "Functional Properties of Oat Proteins Modified by Acylation, Trypsin Hydrolysis or Linoleate Treatment", C. Ma and D. Wood, JAOCS, vol. 64, no. 12, pp. 1726-1731 (1987), it is described that treatment of oat protein with the protease trypsin will break down approx. half of the protein and will result in a protein component with a solubility of between 40 and 60% within the pH range 3-8. These articles do not describe how to produce a protein that is completely stable against precipitation and insolubility. The dry powder produced using the described method is also at most 60% soluble in the pH range 3.5-8.0.

The article "Some Functional and Nutritional Properties of Oat Flours as Affected by Proteolysis", R. Ponnampalam, G. Goulet, J. Amiot and G. Brisson, J. Agric. Food. Chem., vol. 35, No. 2, pp. 279-285 (1987), describes a flour product with a nitrogen protein solubility of a maximum of 50%.

The article "Enzymic Solubilization of Cereal Proteins by Commercial Proteoses", C. Nkonge and C. Ballance, Cereal Chem., vol. 61, No. 4, pp. 316-320

(1984), describes a method for obtaining an oat substrate with a nitrogen solubility of 90%. This article describes the preparation of aqueous slurries that separately contain different grains, including oats. These slurries are made basic by the addition of a base. The aqueous, basic slurry is also treated with certain protease enzymes for a time period of approx. 12 hours. This ensures the recovery of a soluble fraction of the grain from an insoluble fraction. In the case of oat grains, a stable, oat protein-containing solution appears to be used in the described process.

The articles: "Oat Protein Concentrate from a Wet Milling Process: Composition and Properties", J. Cluskey, Y. Wu, J. Wall and G. Inglett, Cereal Chem. 50(4), pp. 481-488 (1979, "Protein Isolate from High-Protein Oats: Preparation, Composition and .Properties", Y. Wu, K. Sexson, J. Cluskey and G. Inglett, J. Food Sei ., vol. 42, no. 5. pp. 1383-1386 (1977), "Oat Protein Concentrates from a Wet Milling Process: Preparation", J. Cluskey, Y. Wu, J. Wall and G. Inglett, Cereal Chem .50(4), pp. 481-488 (1973) and US Patent 4,089,848, all describe the extraction of oat protein from oat products using an alkaline extraction process.

In addition to these methods, oat protein containing products are commercially available. E.g. products Oat CI-40 and Oat CI-15 are available from Canamino, Inc., 118 Veterinary Road, Saskatoon, SK, Canada. The Oat CI-40 product is described as a protein obtained from oats which has a protein content of 40%, is a colourless, beige powder, is dispersible in a number of solvents and has an increased viscosity upon hydration. The Oat CI-15 product is described as a protein obtained from oats which has a protein content of 15%, is a colourless, beige powder, is dispersible in a number of solvents and has an increased viscosity upon hydration. Both of these products can be used in preparations for hair care and skin care such as e.g. bath water, shampoos, creams and gels.

However, the products described above and produced using the methods described above either lack the stability of the product according to the present invention, do not have a high protein concentration, are produced using time-consuming and undesirable production methods, or a combination thereof. Most of these described oat protein fractions are unstable in solution and will fall out of solution upon standing for a period of 1-2 days in cooler conditions. Cooling the preparation containing the soluble oat protein fraction also causes the fraction to precipitate. The products which are stated to be stable are produced in the form of an aqueous preparation which is converted within a time period of 12 hours. This in itself is inefficient and can also cause the growth of microorganisms, making the end product undesirable.

Stable, aqueous preparations containing such oat fractions are also translucent, and their use is therefore limited.

It would thus be desirable to produce a transparent, stable, soluble, oat protein-containing, aqueous solution with a low fat content, and a soluble oat protein fraction which can form such a solution. The present invention provides such a fraction and solution.

It is therefore an object of the present invention to provide a transparent, stable, oat protein-containing, aqueous solution with a low fat content and a dried, solid, stable, oat protein-containing fraction which can be used to produce a transparent, stable, aqueous solution with a low fat content by rehydration . It is also an object of the present invention to provide a method for producing such a solution and fraction.

These and other purposes are accomplished by means of the invention described here.

Unless otherwise stated, all weight percentages are given on a dry weight basis.

The present invention relates to a method for fractionating oats to obtain a transparent, stable, soluble, oat protein-containing, aqueous solution, characterized in that

a) an aqueous slurry comprising water and an oat substrate is prepared, b) the oat substrate is fractionated by maintaining the slurry at a sufficient temperature and treating the slurry with sufficient agitation, sufficient base or acid to adjust the pH of the aqueous slurry to outside the isoelectric range and sufficient protease to hydrolyze sufficient oat protein, thereby obtaining a translucent slurry comprising the insoluble solid fraction, an insoluble liquid fraction, a stable soluble oat protein fraction, a soluble oat fat fraction and a soluble oat carbohydrate fraction and c) the insoluble liquid fraction and the insoluble solid fraction are removed from the slurry, thereby recovering a final transparent, stable,

low fat aqueous solution comprising water and a stable soluble oat protein fraction, a soluble oat fat fraction and a soluble oat carbohydrate fraction.

The present invention further comprises the product from the above method.

The present invention further comprises a solid fraction in purified form containing soluble oat protein.

In the method according to the present invention, an aqueous slurry comprising water and an oat substrate is first prepared. The amount of oat substrate in the slurry depends on how viscous it makes the slurry and the efficiency of the separation process. The concentration of oat substrate in the slurry typically ranges from 1 to 15%, preferably from 5 to 15%, more preferably from 8 to 12% by weight, based on the total weight of the aqueous slurry.

The oat substrate which is usable in the method according to the invention can be in any form from which a soluble fraction can be recovered, can be defatted and can be whole or reduced in size. Examples of usable oat substrates include whole oats both hulled and shelled, defatted, whole oats, whole rolled oats, split oats, defatted split oats, oat flour, defatted oat flour, oat bran, defatted oat bran, oat flour, defatted oat flour, fine oat flour, defatted fine oat flour , oat flakes, defatted oat flakes and mixtures thereof, with oat flour being preferred.

The oat substrate can be reduced in size using any method known to the person skilled in the art. Size reduction methods typically use rubbing, shearing, impact and compression forces. Examples of equipment that is applicable for the size reduction carried out here include, but are not limited to, grinding machines, cereal granulators, hammer mills, pin mills, roller mills, ball mills, grinding mills, "kibblers", air jet mills and granulators, with hammer mills being preferred.

In a more preferred embodiment of the present invention, dehulled oat groats are milled prior to combining the groats with water to form the aqueous slurry of the present invention in a hammer mill into a flour comprising two general particle types. The first particle type is a light, coarse fraction of irregularly shaped particles, preferably with a particle size in the range of from 500 to 3000 µm. A second particle type is a dense, fine fraction of regularly shaped particles, preferably with a particle size in the range of from 100 to 500 µm. The fine fraction is combined with water to form the aqueous slurry of the present invention. A detailed description of methods for grinding oatmeal to obtain these coarse and fine fractions is described in US patent 4,028,468.

As soon as the aqueous slurry is prepared, the oat substrate is fractionated. The oat substrate is fractionated by maintaining the slurry at a sufficient temperature, shaking the slurry, adding acid or base to adjust the pH of the slurry to a value outside the isoelectric range, and treating the slurry with protease. These steps can take place in any order, provided that they follow the preparation of the slurry and are preferably carried out simultaneously.

The slurry is kept at a temperature and for a period of time that is sufficient to fractionate the oat substrate while it is simultaneously shaken and acid or base is added. The temperature is maintained at the required level by means known to those skilled in the art, typically by heating or cooling, the exact means depending on factors such as e.g. the ambient temperature and the required slurry temperature. The slurry is preferably kept at a temperature in the range of from 5 to 70°C, more preferably from 20 to 70°C, even more preferably from 45 to 60°C, and for a period of from 15 to 720, more preferably from 30 to 240, even more preferably from 60 to 180 min. Care must be taken to avoid maintaining the slurry at a temperature that would inactivate the protease enzyme or gelatinize any oat starch present. If the oat starch gelatinizes, it will become soluble, at which point separation from the desired oat protein will become difficult, and the concentration of oat protein in the final product will be reduced.

In the shaking step, the aqueous slurry is shaken by mechanical means for a period of time sufficient, when the shaking is combined with heating and addition of acid or base, to fractionate the oat substrate. The preferred degree of shaking is an amount sufficient to suspend the oat substrate, as well as the respective fractions resulting from the fractionation of the oat substrate. Care must be taken to avoid excessive shaking and the correspondingly high shear force. High shear can act to make the oat starch soluble and can break down the protease enzyme, which, as already mentioned, is undesirable.

In general, any shaking method may be used in the method of the invention, including, but not limited to, propeller agitators, paddle mixers and recirculation pumps, with propeller agitators being preferred. The slurry is preferably stirred with a propeller agitator operating at a speed sufficient to suspend the oat substrate. The exact rate will of course depend on the concentration of oat substrate in the slurry, the size of the vessel in which the slurry is prepared, the slurry temperature, the propeller design, etc., and this will be apparent to those skilled in the art.

The pH of the slurry is adjusted to outside the isoelectric range by adding either an acid or a base. This is necessary to carry out the extraction of oat protein fractions! from the oat substrate. When an acid is used, the extraction is referred to as an acid extraction. When a base is used, the extraction is referred to as an alkaline extraction. The alkaline extraction is preferred.

In an acidic extraction, the amount of acid necessary for the method according to the invention is that required to give the aqueous slurry an acidic pH below the isoelectric range, the preferred pH value depending on the type of protease used. Preferably, the amount used is that which is necessary to adjust the pH of the slurry to within a range of from approx. 1 to approx. 4, more preferably from approx. 1 to approx. 3. Care must be taken to avoid adjusting the pH of the slurry to a level at which the particular protease enzyme or enzymes used in the present invention are inactivated. If the slurry's pH is below 3, it will typically have to be adjusted to above 3 before adding the protease to the slurry.

In general, any food grade acid known to the person skilled in the art can be used in the method according to the invention. Examples of usable acids include, but are not limited to, phosphoric acid, hydrogen chloride, citric acid and mixtures thereof, with phosphoric acid being preferred.

In an alkaline extraction, the amount of base necessary for the method according to the invention is that required to give the aqueous slurry a basic pH, the preferred pH value depending on the type of protease used. The quantity used is preferably that which is necessary to adjust the slurry to a pH value in the range of from approx. 8 to approx. 12, more preferably from approx. 10 to approx. 12.

In general, any food grade base known to the person skilled in the art can be used in the method according to the invention. Examples of usable bases include, but are not limited to, sodium carbonate, sodium hydroxide, calcium hydroxide, ammonium hydroxide and mixtures thereof, sodium carbonate and sodium hydroxide being preferred and sodium hydroxide being most preferred.

The protease used in the present invention is one which will make the soluble oat protein fraction stable, provided that it is combined with the oat substrate prior to fractionation of the substrate. Stable means that the oat protein fraction will not fall out of solution, which typically happens with oat protein. When the aqueous solution according to the present invention is dried, it further gives a dried product comprising the soluble oat fractions already described here. In the dried state, substantially all of the resulting dried product, including the soluble oat protein fraction, will dissolve upon rehydration to form a stable solution. This is a function of the stability of the oat protein fraction. As soon as the oat protein fraction falls out of solution, the fraction is rendered essentially insoluble and will not redissolve upon rehydration. This definition of stable applies to the original aqueous slurry, as well as the purified, soluble, low-fat oat fraction that forms the clear, aqueous solution upon rehydration, and the final, clear, stable, oat fraction-containing, low-fat aqueous solution produced by of the method according to the invention. The protease is not required to extract the oat protein fraction from the oat substrate, as this can be accomplished simply by maintaining a proper slurry temperature and stirring the basic or acidic aqueous slurry. However, the protease is necessary to produce a final stable, soluble oat protein fraction that will not precipitate on storage and will dissolve again on rehydration from a dried state.

The protease is also necessary to increase the yield of soluble oat protein fraction recovered in the final clear aqueous solution of the present invention. If an oat substrate is fractionated without treatment with a protease, the remaining suspension after the insoluble solid fraction is removed comprises a soluble carbohydrate fraction, an unstable soluble oat protein fraction, an insoluble liquid fraction that is primarily oat fat, and an insoluble liquid fraction comprising oat protein in association with oat fat. These insoluble liquids impart a translucency to the aqueous suspension and must therefore be removed to obtain a clear, aqueous solution. If the insoluble liquid fraction comprising oat protein in connection with oat fat is removed, however, the yield of oat protein in the final solution will be undesirably low.

In order to achieve maximum yield of soluble oat protein in the final, aqueous solution from the method according to the invention, the insoluble liquid fraction comprising oat protein in connection with oat fat must be minimized. This is done by dissociating the oat fat from the oat protein. By dissociation, an insoluble, liquid oat fat-containing fraction and a soluble oat protein fraction are obtained. In the original, aqueous slurry according to the invention, the oat protein must therefore be essentially dissociated from the oat fat.

This dissociation is carried out by treating the oat substrate with protease during fractionation as described here. The amount of protease required to dissociate the oat protein from the oat fat is that described herein to render the soluble oat protein fraction stable.

The protease also helps increase the rate at which the stable, soluble oat protein fraction goes back into solution.

The protease enzyme is added after the original slurry has been prepared and is preferably added simultaneously with the heating and stirring of the slurry and the pH adjustment.

Protease enzymes known to be effective in the present invention include, but are not limited to, proteases that act in both alkaline and acidic pH ranges, but have little or no amylase activity, proteases that act in the alkaline pH range preferred. More preferred are the bacterial alkaline proteases which do not have amylase activity and which exhibit lipase and β-glucanase activity. Proteases preferred in the present invention include Optimase\APL-440 and Opticlean\L-1000, both of which are available from Solvay Enzymes, located in Elkhart, Indiana; Alcalase\, available from Novo Nordisk, located in Walton, Connecticut; papain, and mixtures thereof, with Optimase\ and OpticleanY and mixtures thereof being preferred. In an even more preferred embodiment, Opticlean\ and Optimase\ are added in sequence, in connection with pH adjustment in such a way that denaturation of the proteases is prevented.

The amount of protease enzyme necessary for the method according to the invention is that required to produce a stable, soluble oat protein fraction and maximize the yield of the fraction, and will depend on factors such as e.g. the time available for the enzyme to react, the type or types of enzymes used and the pH of the slurry and the degree and time of heating and stirring used. Preferably combined from approx. 0.1 to approx. 10.0, more preferably from approx. 0.25 to approx. 2, even more preferably from approx. 0.40 to approx. 1% by weight, as a percentage of the oat substrate, protease enzyme with the aqueous slurry. The protease is preferably allowed to react with available oat protein in a basic or acidic, heated and stirred, aqueous slurry for a period of time in the range of from 15 to 720, preferably from 30 to 240, more preferably from 60 to 180 min.

When longer reaction times are used, precautions must be taken to inhibit the growth of microbial organisms in the slurry. Any methods known to the person skilled in the art can be used. However, care must be taken to avoid denaturing the protease enzyme. Examples of applicable methods include, but are not limited to, addition of bacterial growth-inhibiting compounds, including sulphite-containing compounds, treatment of the slurry under sterile conditions, adjustment and/or maintenance of working conditions during the process such as e.g. temperature and pressure, so that bacterial growth is inhibited, care being again taken to avoid denaturation of the protease enzyme, and mixtures thereof.

Since it is an aim of the method according to the invention to achieve a final aqueous solution containing a stable, soluble oat protein, it is desirable to achieve the practically maximum oat protein concentration in the final solution. This can be achieved by maximizing the amount of stable, soluble oat protein present in the original aqueous slurry. The soluble oat protein is present in solution in the original slurry, and remains so throughout the entire method according to the invention and is contained in the final, aqueous solution according to the invention. It is thus preferred that there is as great a protein concentration in the original slurry as possible.

The fractionation yields a stable, translucent, aqueous slurry that typically comprises from 60 to 95, more typically from 70 to 90, even more typically from 75% to 85% by weight insoluble solid fraction, from 5 to 10, more typically from 6 to 10, even more typically from 6 wt% to 8 wt% insoluble liquid fraction, from 5 to 20, more typically from 8 to 18, even more typically from 10 wt% to 15 wt% stable soluble oat protein, from 0 to 3, more typically from 0 to 2, even more typically from 0 to 1 wt% soluble oat fat and from 1 to 8, more typically from 1 to 5, even more typically from 3 wt% to 5 wt% soluble oat carbohydrate.

The insoluble solid fraction is primarily starch. It typically contains less than approx. 2% fat by weight, less than approx. 10% by weight protein and more than approx. 75% by weight carbohydrate. When a defatted oat substrate is used, the insoluble fraction is essentially unchanged.

The insoluble liquid fraction is primarily insoluble oat fat. When a defatted oat substrate is therefore used in the production of the original, translucent, aqueous slurry, the concentration of insoluble liquid fraction in the original slurry will be reduced correspondingly by the amount of fat removed to give the defatted oat substrate.

When a defatted oat substrate is used to prepare the starting slurry, the slurry typically comprises from approx. 60 to approx. 95, more typically from approx. 70 to approx. 90, even more typically from ca. 75 to approx. 85% by weight insoluble, solid fraction, from approx. 1 to approx. 5, more typically from approx. 1 to approx. 4, even more typically from ca. 1 to approx. 2 wt% insoluble liquid fraction, from approx. 5 to approx. 20, more typically from approx. 8 to approx. 18, even more typically from ca. 10 to approx. 15% by weight stable, soluble oat protein, from 0 to approx. 3, more typically from 0 to approx. 2, even more typically from 0 to approx. 1% by weight soluble oat fat and from approx. 1 to approx. 8, more typically from approx. 1 to approx. 5, even more typically from ca. 3 to approx. 5 wt% soluble oat carbohydrate.

After the oat substrate is fractionated to form a translucent slurry as described herein, the insoluble liquid and solid fractions are removed from the slurry. The solid and liquid insoluble fractions can be removed in any order. The insoluble solid fraction is preferably removed first to produce a suspension, followed by removal of the insoluble liquid fraction from the suspension to give an aqueous solution.

The insoluble solid fraction can be removed from the slurry by any method known to the person skilled in the art, preferably by physical separation. Examples of physical separation methods useful for removing the insoluble solids fraction from the slurry include, but are not limited to, centrifugation, microfiltration, a molecular sieve, a settling pond, and combinations thereof, with centrifugation being preferred. The centrifugation can be carried out using any method and any centrifuge equipment known to the person skilled in the art. Examples of centrifuge equipment useful for removing the insoluble solids fraction in the present invention include, but are not limited to, disk separators, decanting centrifuges, only/centrifuges and batch centrifuges, with decanting centrifuges being preferred. More preferably, the slurry containing the insoluble solids and the liquid fractions is centrifuged in a decanting centrifuge at a gravity of at least approx. 24,500 m/s<2> (2500 G), more preferably at least approx. 29,400 m/s<2> (3000 G), even more preferably at least approx. 34,300 m/s<2> (3500 G) for a period of at least approx. 1 min., preferably at least approx. 2 min., even more preferably at least 3 min., thereby removing the insoluble solid fraction from the slurry and giving a suspension comprising the insoluble liquid fraction and the soluble fractions.

Typically, at least approx. 80%, more typically at least approx. 90%, even more typically at least approx. 95% by weight of available, insoluble solids fraction from the slurry.

The insoluble liquid fraction primarily comprises oat fat. This insoluble fat can be removed from the slurry either by means of physical separation techniques, by conversion to a water-soluble form, which then remains in solution with the remaining soluble oat protein fraction, or a combination thereof, physical separation being preferred.

Although not tested, it is likely that at least a portion of the insoluble fat can be removed from the translucent slurry by conversion of the insoluble fat to water-soluble fatty acids by treatment with a lipase enzyme. A part of the resulting fatty acids are water-soluble and can form a solution, in contrast to the suspension of insoluble fat that occurs during fractionation of the oat substrate. Once the fatty acids are in solution, they will remain in solution with the soluble oat protein fraction after separation of the insoluble material from the slurry.

The lipase treatment of the insoluble fat can be carried out at any time after the aqueous slurry is prepared, and can be carried out together with stirring and heating, pH adjustment and the protease treatment, preferably after the oat substrate is fractionated and before separation of any insoluble material. The amount of lipase required to reduce the insoluble fat to fatty acids will be easily determined by the person skilled in the art, and should vary from approx. 0.1 to approx. 10%, more typically from approx. 0.25 to approx. 2%, even more typically from approx. 0.25 to approx.

1% by weight, based on the weight of the starting oat substrate used to prepare the starting aqueous slurry. The lipase treatment can also be carried out by treating the oat substrate with a protease enzyme that has lipase activity. Any remaining, insoluble liquid fat and insoluble fatty acids that remain after the lipase treatment can be removed by physical separation as described here.

In the preferred embodiment where the insoluble solid fraction is first removed from the slurry to form a suspension and after the solid fraction is removed, the resulting suspension is concentrated and then subjected to a physical separation process.

Examples of methods useful herein for concentrating the suspension include, but are not limited to, evaporation, reverse osmosis, freeze concentration, membrane filtration, ultrafiltration, and mixtures thereof, with evaporation being preferred, and evaporation using heat and a vacuum being even more preferred .

The suspension is preferably concentrated to a solids concentration of at least approx. 5%, more preferably at least approx. 10%, even more preferably at least approx. 15% by weight, expressed as a percentage of the total suspension, and is heated and/or kept at the same time at a temperature of at least approx. 25°C, more preferably at least approx. 40°C, even more preferably at least approx. 50°C.

The physical separation of the insoluble liquid fraction can be carried out using any method known to the person skilled in the art. Examples of physical separation methods applicable herein include, but are not limited to, centrifugation, microfiltration, a molecular sieve, a settling pond, mixtures thereof, with centrifugation and microfiltration, and mixtures thereof being preferred, and centrifugation followed by microfiltration being more preferred. Another separation method that can be used is to absorb the insoluble liquid fat into the insoluble starch and remove both by the physical separation of the insoluble solid material.

The centrifugation of the suspension containing the insoluble liquid fraction can be carried out using any method and any centrifuge equipment known to the person skilled in the art. Examples of centrifuge equipment that can be used here include, but are not limited to, disk separators, decanting centrifuges, basket centrifuges and batch centrifuges, disk separators being preferred. In a preferred centrifugation method, the suspension is heated to and/or maintained at a minimum temperature of approx. 25°C, preferably approx. 40°C, more preferably approx. 50°C, and then introduced into a liquid/liquid disc separator. The separator is operated at a minimum of approx. 24,500 m/s<2> (2,500 G), preferably approx. 29,400 m/s<2> (3000 G), more preferably approx. 34,300 m/s<2> (3500 G). The residence time for the suspension in the separator is in the range of approx. 1 to approx. 10 min., preferably from approx. 2 to approx. 5 min., more preferably from approx. 2 to approx. 3 min.

The microfiltration array can be carried out using any method and any filtration equipment known to the person skilled in the art. Examples of microfiltration equipment that can be used in the present invention include, but are not limited to, spiral membrane systems, pipe systems, ceramic membranes and stainless steel membranes, spiral membrane systems being preferred.

After concentration and centrifugation, the suspension is heated in a preferred microfiltration method to and/or kept at a temperature of at least approx. 25°C, more preferably at least approx. 40°C, even more preferably at least approx. 50°C. The heated and concentrated suspension is introduced into a helical microfilter element. The filter is operated at a transmembrane pressure in the range of approx. 3.4 to about 34 kPa (5 to 50 psi), preferably from 6.9 to about 20.7 kPa (10 to about 30 psi), more preferably from about 6.9 to about 13.8 kPa (10 to 20 psi).

In the physical separation method, at least approx. 80%, more typically at least approx. 90%, more typically at least approx. 95% by weight of the available, insoluble liquid fraction from the slurry and/or suspension.

The term suspension, as used herein, refers to an aqueous mixture in which the particulate matter remains in suspension in the aqueous environment, and is not deposited. This is in contrast to a slurry, which as used herein refers to an aqueous mixture in which the particulate matter will not remain in suspension, but will settle in the absence of agitation or other means of carrying the particulate matter. The term solution has its normal meaning as understood by the person skilled in the art.

The final clear aqueous solution of the present invention typically comprises from 30 to 80, more typically from 40 to 70, more typically from 50% to 60% by weight stable, soluble oat protein, from 0 to 3, more typically from 0 to 2 , even more typically from 0 to 1 wt% soluble oat fat and from 10 to 40, more typically from 15 to 35, even more typically from 20 wt% to 30 wt% soluble oat carbohydrate and typically contains a maximum of 0.5, preferably 0 .2, even more preferably 0.1 vol% remaining insoluble material. The final, transparent, aqueous solution may further comprise soluble fatty acids, if part of the insoluble, liquid fat is converted into fatty acids, although this is not preferred.

To achieve a transparent, aqueous solution, the size of any insoluble material present in the solution must be minimal, so as not to scatter or diffuse light. The maximum particle size for the remaining insoluble material in the final, clear, low-fat aqueous solution of the present invention is typically about 1, preferably approx. 0.2, more preferably approx. 0.1 //rn.

In a preferred embodiment of the present invention, the final, oat protein-containing, aqueous solution is treated to prevent the growth of bacteria. This will give a product that will be microbiologically stable. Microbiological stability is different from the phase stability already discussed here, and can therefore be stored and used by consumers for longer periods of time. The treatment methods that can be used will be known to the person skilled in the art. Examples of applicable methods include, but are not limited to, lowering the water activity of the solution, e.g. by drying the solution to obtain a solid residue or adding a solvent such as propylene glycol, addition of bactericides to the aqueous solution, acid treatment, lowering the temperature of the solution and mixtures thereof, lowering the water activity being preferred. In a more preferred embodiment, the water activity is lowered to a maximum level of approx. 0.65, more preferably approx. 0.60, even more preferably approx. 0.50.

A preferred method according to the present invention comprises: a) grinding oat groats to form an oat flour containing a dense, fine fraction of regularly shaped particles and a light, coarse fraction of irregular

shaped particles, where the fine fraction comprises oat protein,

oat carbohydrate and fat,

b) preparing an aqueous slurry comprising from 8% by weight to 12% by weight of the fine oat flour fraction, c) dissolving the soluble fraction from the fine oat flour fraction by heating the aqueous slurry to a temperature in the range of

from 45 to 60°C in connection with stirring for a period of time in the range of from 60 to 180 min., with simultaneous treatment of the aqueous slurry

with from 0.4% to 1% by weight, based on the weight of the fine oat flour, of a mixture of protease enzyme added sequentially in the respective order, and

sufficient sodium hydroxide to adjust the initial pH of the slurry to within the range of from 10 to 12, thereby obtaining a slurry comprising from 75% by weight to 85% by weight of an insoluble solid fraction, from 6% by weight to 8% by weight of an insoluble liquid fraction , from 10% by weight to 15% by weight of a stable, soluble oat protein fraction with a minimum solubility of 90%, from 3% by weight to 5% by weight of a soluble oat carbohydrate fraction and from 0

wt% to 1 wt% of a soluble oat fat fraction,

d) centrifugation of the slurry at a minimum gravity of approx. 34,300 m/s<2> (3500 G) for a period of at least approx. 3 min., thereby removing

at least approx. 95% by weight of the available, insoluble, solid fraction and obtain an aqueous suspension containing the soluble oat fractions and

the insoluble liquid fraction,

e) concentrating the suspension to a concentration of at least approx. 15% by weight solids, and heating and/or maintaining the suspension at a

temperature of at least 50°C, and

f) separation of the insoluble liquid fraction by liquid/liquid disc separation at a gravity of at least 34,300 m/<2> (3500 G) or a

time period in the area of from approx. 2 to 3 min., followed by microfiltration in a helical microfilter element operating at a transmembrane pressure in the range of 6.9-13.8 kPa (10-20 psi), thereby recovering a clear aqueous solution comprising water, from 50 wt% to 60 wt% stable soluble oat protein fraction, from 20 wt% to 30 wt% soluble oat carbohydrate and from 0 wt% to 1 wt% soluble oat fat, and containing a maximum of 0.1 vol% of residual insoluble material.

Also preferred is the product which is produced using the aforementioned, preferred method.

The method according to the present invention provides a significant yield of recovered, soluble oat protein fraction, based on the starting weight of the oat substrate. It is naturally preferable to achieve a maximum yield. In the present invention, the yield is typically in the range of from approx. 10 to approx. 30%, more typically from approx. 15 to approx. 30%, even more typically from approx. 15 to approx. 25%.

The present invention also includes the product which is soluble in aqueous solution, produced using the method according to the invention as already described here.

The present invention also comprises a final solid, i.e. dried, mixture comprising the stable, soluble oat protein fraction, the soluble oat fat fraction and the soluble oat carbohydrate fraction as already described here, included in the same relative concentrations. The solid mixture is obtained by drying the final aqueous solution according to the present invention to a moisture level not higher than approx. 12%, preferably approx. 10%, even more preferably approx. 8% by weight. The purified solid mixture has an oat protein solubility in solution of at least 70%, preferably at least 85%, more preferably at least 95%. The solubility is determined according to the nitrogen solubility method set forth in the work "Protein Isolate from High Protein Oats: Preparation, Composition and Properties", Y. Wu, K. Sexson, J. Cluskey and G. Inglett, J. Food Sei., vol . 42, No. 5, pp. 1383-1386 (1977). The final stable, soluble oat protein fraction from the method according to the present invention, including its dried form and when present in solution as described above, can also be characterized by its molecular properties. The soluble oat protein has a molecular weight of less than approx. 30,000, preferably less than 10,000, more preferably less than 3,000. The molecular weight is a factor in the degree of treatment of the original oat substrate with a protease enzyme during fractionation, as already described here.

While not intended to be bound by any theory, it is unexpected and surprising that a transparent, stable, oat protein-containing solution can be prepared from an oat substrate using the method according to the invention. It has not been described or suggested that the fat in the form of an insoluble liquid can be separated from the soluble oat protein fraction, thereby providing a transparent, stable, oat protein-containing, aqueous solution. It is also unexpected and surprising that the resulting oat protein-containing mixture will give a clear, stable solution upon rehydration, when in the dried state.

The present invention is further illustrated by the following examples.

Example 1

The fine fraction of oat flour is slurried with soft water in a ratio of 1:10 parts by weight. The slurry is heated to 55-60°C and stirred. 2% sodium carbonate (Na2C03) by weight of oat flour is added to the slurry to adjust the pH to 9.5-10.5. Finally, 1% protease enzyme (Optimase) by weight of the oat flour is added to the slurry. The slurry is kept at 55-60°C with gentle stirring for 1-2 hours, thereby fractionating the oat flour into an insoluble, solid fraction, an insoluble liquid fraction, a soluble oat protein fraction, a soluble oat fat fraction and a soluble oat carbohydrate fraction. The slurry is then centrifuged at 31,400 m/s<2> (3200 G) for 3 min. to separate the insoluble solid fraction, which gives an aqueous suspension containing an insoluble liquid fraction, a soluble oat protein fraction, a soluble oat fat fraction and a soluble oat carbohydrate fraction. The soluble, oat protein-containing suspension is then neutralized with phosphoric acid to a pH value of 6-6.5. The suspension is then concentrated in a falling film evaporator from a starting solids level of approx. 2-2.5% to 15-20% solids.

The concentrated suspension is then heated to 50-60°C and centrifuged using a liquid/liquid separator which is usually used for separating cream from milk. Two streams are obtained from this separator, a light phase containing 25-40% insoluble oil and a heavy phase containing the soluble oat protein. Next, the heavy phase (oat protein suspension) is treated using a helical microfiltration system with a nominal pore size of 0.1 µm. The system is operated at 50-55°C with a transmembrane pressure of 6.9-13.8 kPa (10-20 psi) The solution passing through the filter (permeate) is then concentrated and spray-dried to give a dark powder with a protein content of 50 -60% and a fat content of less than 1%. The powder can be mixed with water to obtain a 2-5% aqueous solution (by weight) which is transparent and does not separate on standing.

Example 2

Oat flakes are mixed with water in a ratio of 1:12 parts by weight. The slurry is heated to 55-60°C and stirred. Two percent (2%) sodium carbonate (Na2C03) by weight of oat flakes is added to the slurry to adjust the pH to 9.5-10.5. At the same time, 0.5% protease enzyme (Optimase\) by weight of oat flour is added to the slurry. The slurry is kept at 55-60°C with gentle stirring for 1-2 hours, thereby fractionating the oat flour into an insoluble solid fraction, an insoluble liquid fraction, a soluble oat protein fraction, a soluble oat fat fraction and a soluble oat carbohydrate fraction. The slurry is then centrifuged at 31,400 m/s<2> (3200 G) for 2-3 min. to separate the insoluble solid fraction, yielding an aqueous suspension containing an insoluble liquid fraction, a soluble oat protein fraction, a soluble oat fat fraction and a soluble oat carbohydrate fraction. The soluble, oat protein-containing suspension is neutralized with any food acid such as e.g. phosphoric acid to a pH value of 6-7. The suspension is then concentrated in a falling film evaporator from an initial solids level of 1.5-2.0% to 5-10% solids by weight. This aqueous suspension is heated to 45-55°C and fed to a helical filter with a nominal pore size of 0.1 µm. The system is operated at a transmembrane pressure of 6.9-13.8 kPa (10-20 psi). The solution that passes through the filter (permeat) contains the soluble oat protein. This permeate is concentrated in an evaporator and spray dried to give a brown powder. The powder has a protein content of 50-60% and a fat content of less than 1%. When this powder is rehydrated in water to form a 2-5% by weight solution, the solution is transparent and does not separate on standing. The yield of oat protein powder is 10-15% based on the initial oat flour weight.

Example 3

Whole oat flour is slurried with soft water in a ratio of 1 part by weight of flour to 10 parts by weight of water. 1.5% by weight NaOH calculated on the oatmeal is added to the slurry to adjust the pH of the slurry to 11-12. The slurry is heated to 50°C and stirred. After 1 hour, 0.5% alkaline protease enzyme (Opticlean\) is added to the slurry. The slurry is kept at 50°C for 30-60 min. with gentle stirring. pH drops to 10-11. Then 0.5% protease enzyme (OptimaseV) is added to the slurry and kept at 50°C with mixing for 30-60 min., thereby giving an aqueous slurry containing an insoluble solid fraction, an insoluble liquid fraction, a soluble oat protein fraction , a soluble oat fat fraction and a soluble oat carbohydrate fraction. The slurry is then centrifuged at 39,800 m/s<2> (4000 G) for 2-3 min. to remove the insoluble solid fraction, yielding an aqueous suspension containing an insoluble liquid fraction, a soluble oat protein fraction, a soluble oat fat fraction and a soluble oat carbohydrate fraction. The aqueous suspension containing oat protein is neutralized with phosphoric acid to a pH value of 6-7. The suspension is concentrated in a falling film to 10-20% solids. This suspension is heated to 50-60°C and fed to a liquid/liquid separator which is typically used for separating cream from milk. This separator produces a light phase containing 25-50% oil and a heavy phase containing the soluble oat protein. The heavy phase is pumped through a helical ultrafilter with a molecular weight cutoff of 500,000 to remove suspended matter and provide a clear, aqueous solution containing soluble oat protein, soluble oat fat and soluble oat carbohydrate. This solution is the permeate from the filter (ie it passes through the filter). This permeate is then concentrated and spray dried to give a brown colored powder containing 50-65% protein and less than 1% fat. When this powder is rehydrated with water to form a solution with 2-10% solids, the solution is transparent and does not settle on standing. The brown powder, which is the oat protein fraction with a low fat content, represents 15-25% of the weight of the starting oat flour.

Example 4

Fine oat flour is slurried with water in a ratio of 1 part by weight of flour to 10 parts by weight of water. 2% by weight of sodium carbonate (Na2CC"3) and 1% by weight of papain calculated for the oatmeal are added to the slurry, which is then heated to 55-60°C, stirred and kept for 18 hours, thereby fractionating the oatmeal into an insoluble, solid fraction, an insoluble liquid fraction, a soluble oat protein fraction, a soluble oat fat fraction, and a soluble oat carbohydrate fraction.The slurry is then centrifuged at 34,300 m/s<2> (3500 G) for 2-3 minutes to separate the insoluble solid fraction, yielding an aqueous suspension containing an insoluble liquid fraction, a soluble oat protein fraction, a soluble oat fat fraction and a soluble oat carbohydrate fraction. The aqueous suspension is then neutralized with acid to a pH of 5-7 and concentrated to 8-15% solids using reverse osmosis in a spiral membrane system (Separatech Membrane NF45, Separation Technology, Inc., St. Paul, MN).This suspension is then treated using a spiral microfiltration system with a nominal pore size e of 0.1 jc/rn. The system is operated at 25-30°C with a transmembrane pressure of 6.9-13.8 kPa (10-20 psi). The solution that passes through the microfilter (permeat) contains the soluble oat protein and is transparent. This solution is evaporated using a falling film evaporator to 20-40% solids and then spray dried. The spray-dried powder is brown in color and contains 5-10% moisture, 50-70% protein, 5-15% ash and less than 1% fat. When this powder is rehydrated with water to prepare a solution, the solution is transparent and does not separate on standing.

Example 5

The fine oat flour fraction is slurried with water in a ratio of 1 to 10 parts by weight. To this slurry, add 2% by weight of sodium carbonate and 1% by weight of Alcalase\enzyme calculated for the oat flour. The slurry is heated to 55-60°C, stirred and kept for 18-24 hours. The slurry is then centrifuged at 34,300 m/s<2> (3500 G) for 5-10 min. to give a clear, liquid solution and a solid, insoluble material. The aqueous solution is freeze-dried to yield a brown powder containing 10-20% stable, soluble protein. On rehydration with water, the resulting solution is transparent and does not separate on standing.

Example 6

Oat flakes are slurried in water in a ratio of 1 part by weight of flakes to 10 parts by weight of water. The slurry is heated to 50-55°C while at the same time 2% by weight sodium carbonate and 1% by weight Alcalase\ calculated on the weight of the oat flakes are added. The slurry is stirred and kept at 50-55°C for 2-4 hours, thereby fractionating the oat flour into an insoluble solid fraction, an insoluble liquid fraction, a soluble oat protein fraction, a soluble oat fat fraction and a soluble oat carbohydrate fraction. The slurry is then centrifuged at 34,300 m/s<2> (3500 G) for 5-10 min. to remove the insoluble solid fraction, yielding an aqueous suspension containing an insoluble liquid fraction, a soluble oat protein fraction, a soluble oat fat fraction and a soluble oat carbohydrate fraction. This suspension is then run through a helical microfiltration system with a nominal pore size of 0.1 µm at an operating temperature of 50-55°C and a transmembrane pressure of 6.9-13.8 kPa (10-20 psi). The aqueous solution that passes through the filter (permeate) contains the soluble oat protein and is transparent. This permeate is then concentrated to 20-40% solids in a falling film evaporator and spray dried. The resulting powder is brown in color and contains 5-10% moisture, 10-25% protein and less than 10% fat. After rehydration in water, the resulting solution is transparent and does not separate on standing.

Claims (16)

1. Process for fractionating oats to obtain a transparent, stable, soluble, oat protein-containing, aqueous solution, characterized in that a) an aqueous slurry comprising water and an oat substrate is prepared, b) the oat substrate is fractionated by keeping the slurry at a sufficient temperature and treating the slurry with sufficient agitation, sufficient base or acid to adjust the pH of the aqueous slurry beyond the isoelectric range and sufficient protease to hydrolyze sufficient oat protein, thereby obtaining a translucent slurry comprising an insoluble solid fraction, an insoluble liquid fraction , a stable soluble oat protein fraction, a soluble oat fat fraction and a soluble oat carbohydrate fraction and c) the insoluble liquid fraction and the insoluble solid fraction are removed from the slurry, thereby recovering a final clear, stable, low-fat aqueous solution comprising water and a stable , soluble oat protein fraction, a soluble oat fat fraction and a soluble oat carbohydrate fraction. 2. Method according to claim 1, characterized in that the concentration of oats in the slurry varies from 1% by weight to 15% by weight, based on the total weight of the aqueous slurry. 3. Method according to claim 1 or 2, characterized in that the oat substrate is reduced in size by grinding in a hammer mill to form oat flour, fine oat flour, oat flakes and mixtures thereof. 4. Method according to claim 3, characterized in that the oat substrate is reduced in size to form an oat flour containing a dense, fine fraction of regularly shaped particles and a light, coarse fraction of irregularly shaped particles, where the fine fraction comprises oat protein and oat carbohydrate and where the fine the fraction is recovered from the coarse fraction and fractionated. 5. Method according to any one of claims 1-4, characterized in that the aqueous slurry is kept at a temperature in the range of from 45 to 60°C for a time period in the range of from 60 to 180 min. 6. Method according to any one of claims 1-5, characterized in that the aqueous slurry is made basic by the addition of a base selected from the group comprising sodium carbonate and sodium hydroxide, and mixtures thereof, and where the aqueous slurry has a pH value in the range of from 10 to 12.. 7. Method according to any one of claims 1-6, characterized in that from 0.40% by weight to 0.60% by weight of protease enzyme, as a percentage of the oat substrate, is added to the aqueous slurry and allowed to react with available oat protein in a time period in the range of 60 to 180 min. 8. Method according to claim 7, characterized in that the aqueous slurry comprises from 75% by weight to 85% by weight insoluble solid fraction, from 6% by weight to 8% by weight insoluble liquid fraction, from 10% by weight to 15% by weight stable, soluble oat protein , from 0 wt% to 1 wt% soluble oat fat and from 3 wt% to 5 wt% soluble oat carbohydrate. 9. Method according to any one of claims 1-8, characterized in that the insoluble, solid fraction is removed by centrifuging the slurry in a decanting centrifuge operated at a minimum of 29,400 m/s<2> (3000 G) for a period of at least approx. 2 min., and the insoluble liquid fraction is then removed by concentrating the suspension to a solids concentration of at least approx. 10% by weight and heating the suspension to a temperature of at least 40°C and centrifuging the suspension in a liquid/- liquid separator which is operated at a minimum of 29,400 m/s<2> (3000 G) for a period of time in the range of from approx. 2 to approx. 5 min. and filtered in a helical microfilter element that works at a transmembrane pressure in the range of 6.9-13.8 kPa (10-20 psi). 10. Method according to claim 9, characterized in that the final, transparent, aqueous solution comprises from 50 wt% to 60 wt% stable, soluble oat protein, from 0 wt% to 1 wt% soluble oat fat and from 20 wt% to 30 wt% soluble oat carbohydrate, and contains a maximum of 0.1 vol% of residual insoluble material. 11. Method according to any one of claims 1-10, characterized in that after separation from the insoluble fraction, the final, transparent, soluble, oat protein-containing, aqueous solution is stabilized to prevent the growth of bacteria. 12. Stable, soluble oat protein fraction, characterized in that it is produced using the method comprising: a) grinding oat groats to form an oat flour containing a dense, fine fraction of regularly shaped particles and a light, coarse fraction of irregularly shaped particles, where the fine fraction comprises oat protein, oat carbohydrate and fat, b) preparation of an aqueous slurry comprising from 8% by weight to 12% by weight of the fine oat flour fraction, c) dissolving the soluble fraction from the fine oat flour fraction by heating the aqueous slurry to a temperature in the range of from 45 to 60°C in conjunction with stirring for a period of time in the range of from 60 to 180 min., with simultaneous treatment of the aqueous slurry with from 0.4% by weight to 1% by weight, based on the weight of the fine oat flour, of a mixture of protease enzyme added sequentially in respective order, and sufficient sodium hydroxide to adjust the initial pH of the slurry to within the range of from 10 to 12, thereby obtaining a slurry comprising from 75% by weight to 85% by weight of an insoluble solid fraction, from 6% by weight to 8% by weight of an insoluble liquid fraction, from 10% by weight to 15% by weight of a stable, soluble oat protein fraction with a minimum solubility of 90%, from 3 wt% to 5 wt% of a soluble oat carbohydrate fraction and from 0 wt% to 1 wt% of a soluble oat fat fraction, d) centrifugation of the slurry at a minimum gravity of approx. 34,300 m/s<2> (3500 G) in a period of at least approx. 3 min., thereby removing at least approx. 95% by weight of the available, insoluble, solid fraction and obtain an aqueous suspension containing the soluble oat fractions and the insoluble liquid fraction, e) concentrating the suspension to a concentration of at least approx. 15% by weight solids, and heating and/or maintaining the suspension at a temperature of at least 50°C, and f) separating the insoluble liquid fraction by liquid/liquid disc separation at a gravity of at least 34,300 m/<2> (3500 G ) or a time period in the area of from approx. 2 to 3 min., followed by microfiltration in a helical microfilter element operating at a transmembrane pressure of . the range of from 6.9-13.8 kPa (10-20 psi), thereby recovering a clear aqueous solution comprising water, from 50 wt% to 60 wt% stable, soluble oat protein fraction, from 20 wt% to 30 wt% % soluble oat carbohydrate and from 0 wt% to 1 wt% soluble oat fat, and containing a maximum of 0.1 vol% of remaining insoluble material. 13.. Stable, soluble oat protein fraction according to claim 12, characterized in that it comprises from 50 wt% to 60 wt% stable, soluble oat protein, from 0 wt% to 1 wt% soluble oat fat and from 20 wt% to 30 wt% soluble oat carbohydrate , and contains a maximum of 0.1 vol% of residual, insoluble material. 14. Stable, soluble oat protein fraction with a low fat content in a purified form, characterized in that it comprises from 10% by weight to 40% by weight of soluble oat carbohydrate, from 0% by weight to 3% by weight of soluble oat fat and from 30% by weight to 80% by weight stable, soluble oat protein, where said soluble oat protein fraction has a maximum particle size of insoluble material in solution of approx. 0.2 µm and wherein said fraction provides a clear, aqueous solution when brought into solution with water. 15. Stable, soluble oat protein fraction according to claim 14, characterized in that the soluble oat protein fraction has a solubility of at least approx. 85%. 16. Stable, soluble oat protein fraction according to claim 15, characterized in that it comprises from 20 wt% to 30 wt% soluble oat carbohydrate, from 0 wt% to 1 wt% soluble oat fat and from 50 wt% to 60 wt% stable, soluble oat protein, wherein said fraction has a maximum particle size for insoluble material in solution of 0.1 pm.